Bill has a budget of $320 and consumes three commodities whose unit prices are $4, $5, $6. Write down the equation of his budget plane. The optimal bundle is determined by the tangency condition:
a) 4x + 5y + 6z = 320, tangent to indifference curves
b) 4x + 5y + 6z = 320, tangent to the budget line
c) 4x + 5y + 6z = 320, tangent to the production possibilities frontier
d) 4x + 5y + 6z = 320, tangent to isoquant curves